Vitamin C plays a hands-on role in dozens of processes throughout your body, from building the protein that holds your skin together to helping white blood cells hunt down infections. It’s an essential nutrient, meaning your body can’t make it, so every milligram has to come from food or supplements. Adults need 75 to 90 mg per day, and most people hit that target easily through fruits and vegetables.
It Builds and Maintains Your Skin
Collagen is the most abundant protein in your body. It gives structure to your skin, tendons, ligaments, and blood vessels. Vitamin C is required for a critical step in collagen production: it helps stabilize the collagen molecule so it can hold its shape outside the cell. Without enough vitamin C, collagen becomes unstable and breaks down, which is why severe deficiency (scurvy) causes bleeding gums, slow wound healing, and skin that bruises easily.
Even at levels well above deficiency, vitamin C supports ongoing skin repair. Your skin actively concentrates it, and higher intake is associated with better skin appearance and faster wound closure. This is the reason vitamin C shows up in so many topical serums, though eating it matters just as much for the collagen your body builds from the inside.
How It Supports Your Immune System
White blood cells called neutrophils are your body’s first responders to infection. They move toward invaders, engulf them, and destroy them with a burst of toxic chemicals. Neutrophils stockpile vitamin C at concentrations 10 to 20 times higher than what’s circulating in your blood, and they ramp up their intake even further during active infection. That concentrated vitamin C helps protect the neutrophil itself from the chemical damage it generates while killing pathogens.
Vitamin C also improves how well these cells move toward a threat. In one study, people who increased their vitamin C intake through diet saw a 20% improvement in neutrophil movement toward infection sites. This doesn’t mean megadoses will supercharge your immune system, but it does mean that running low on vitamin C leaves your immune cells slower and less effective.
Does It Actually Shorten Colds?
The largest review of the evidence, a Cochrane analysis covering nearly 10,000 cold episodes, found that taking vitamin C regularly (before you get sick, not after) shortened colds by about 8% in adults and 14% in children. For kids taking 1 to 2 grams per day, the reduction was 18%. In practical terms, that might turn a week-long cold into six days.
The catch: starting vitamin C after symptoms appear doesn’t seem to help. The review found no consistent benefit from taking it therapeutically once a cold has already started. The modest protective effect only showed up in people who were already supplementing daily before they caught the virus.
It Recycles Other Antioxidants
Your body constantly deals with free radicals, unstable molecules that damage cells, DNA, and proteins. Vitamin C neutralizes several types of free radicals directly, but it also plays a less obvious role: it recharges vitamin E after vitamin E has done its own antioxidant work.
Here’s how that works. Vitamin E sits in your cell membranes and intercepts free radicals that would otherwise damage fats in those membranes. But once vitamin E neutralizes a radical, it becomes partially oxidized and loses its protective ability. Vitamin C steps in and donates electrons to restore vitamin E back to its active form. Research in liver cells showed that vitamin C reduced the accumulation of spent vitamin E by 35%, confirming it genuinely recycles vitamin E rather than simply slowing its breakdown. This teamwork means your body gets more mileage out of both vitamins when they’re both present in adequate amounts.
Blood Vessel Health
The inner lining of your blood vessels, called the endothelium, produces nitric oxide, a molecule that relaxes and widens blood vessels. When that lining is damaged by oxidative stress, nitric oxide production drops, blood vessels stiffen, and cardiovascular risk goes up. Vitamin C protects the endothelium from oxidative damage and helps maintain nitric oxide availability, keeping vessels more flexible and responsive.
This doesn’t mean vitamin C supplements prevent heart disease on their own. But consistent intake through food supports the basic vascular function that keeps blood pressure in check and blood flowing smoothly.
It Helps You Absorb Iron
Iron from plant sources (beans, spinach, lentils, fortified cereals) is harder for your body to absorb than the iron in meat. Vitamin C dramatically changes that equation. When researchers added increasing amounts of vitamin C to a meal containing plant-based iron, absorption jumped from 0.8% all the way to 7.1%, nearly a ninefold increase. If you eat a mostly plant-based diet or have been told your iron is low, pairing iron-rich foods with something high in vitamin C (citrus, bell peppers, strawberries) is one of the simplest and most effective strategies to improve absorption.
How Much You Need
The recommended daily amount is 90 mg for men and 75 mg for women. Smokers need an additional 35 mg per day because smoking accelerates vitamin C depletion. Pregnancy and breastfeeding also increase requirements modestly.
A single medium orange provides about 70 mg, a cup of strawberries around 85 mg, and a cup of raw red bell pepper over 190 mg. Most people eating a reasonable amount of fruits and vegetables meet their needs without thinking about it. Supplements are an option if your diet is limited, but your body absorbs vitamin C from food efficiently and in the context of other beneficial compounds.
What Happens if You Take Too Much
Vitamin C is water-soluble, so your kidneys flush out what you don’t need. That built-in safety valve means toxicity is rare, but high doses (typically above 2,000 mg per day) can cause diarrhea, nausea, and stomach cramps. At very high intakes over time, excess vitamin C is converted to oxalate, which can increase the risk of kidney stones in people who are already prone to them. For most people, staying under 2,000 mg a day avoids any issues, and there’s little evidence that doses above a few hundred milligrams provide additional benefit since absorption efficiency drops sharply as intake rises.